For example, a method for sharpening an edge of an object or a texture within an image is known as a technique of correcting a hand tremor (a tremor caused by a move of a subject is not included here) of a shot image.
In normal cases, a pixel value (such as brightness, intensity or the like) changes abruptly at an edge of an object or a texture within an image. A profile illustrated in FIG. 1 represents a change in a pixel value (brightness level here) of an edge. A horizontal axis of the profile represents a position of a pixel. Since the brightness level ramps up and down at an edge, an area including the edge is sometimes referred to as a ramp area in this specification.
To sharpen an edge, for example, as illustrated in FIG. 1, a brightness level of each pixel is decreased in an area (area A) where the brightness level is lower than a central level, whereas the brightness level of each pixel is increased in an area (area B) where the brightness level is higher than the central level. Note that the brightness level is not corrected outside the ramp area. With such corrections, the width of the ramp area is narrowed to sharpen the edge. This method is disclosed, for example, by J.-G Leu, Edge sharpening through ramp width reduction, Image and Vision Computing 18(2000) 501-514.
Additionally, an image processing method for correcting a blur in an image where only some of areas are blurred is proposed as a related technique. Namely, edge detection means detects an edge in eight different directions in a reduced image. Block partitioning means partitions the reduced image into 16 blocks. Analysis means determines whether or not an image of each of the blocks is a blurred image, and detects blur information (a blur width L, the degree of a blur, and a blur direction) of a block image that is a blurred image. Parameter setting means sets a correction parameter based on the blur information, and sets a correction intensity α according to the blur width L (For example, Japanese Laid-open Patent Publication No. 2005-332381).
However, an unnatural image is sometimes obtained if all edges are sharpened. Additionally, since an unnecessary correction is performed in this case, processing time sometimes increases. Furthermore, with the method for setting the correction intensity according to the blur width, a change in the brightness of an edge is corrected too sharply, making a shade too noticeable or enhancing the concavity and convexity of a human face to look wrinkled in some cases. Namely, image quality is sometimes degraded with the blur correction.